Conventional bearing apparatuses including bearing surfaces that move relative to one another are known in the art. For example, conventional, so-called “thrust bearings” and some embodiments of radial bearings include bearing surfaces that at least partially contact and move or slide relative to one another. Such bearing surfaces may include a superhard material for resisting wear during use of the bearing. In one example, diamond (e.g., polycrystalline diamond) may comprise at least one or both of the bearing surfaces.
More particularly, one application for thrust bearings is drilling equipment utilized in the subterranean drilling arts. Particularly, drilling motors have been utilized for drilling boreholes into a subterranean formation, especially for oil or gas exploration. In a typical downhole drilling motor, the motor is suspended at the lower end of a string of drill pipe comprising a series of pipe sections connected together at joints and supported from the surface. A rotary drill bit (e.g., a fixed cutter drill bit, roller cone drill bit, a reamer, etc.) may be supported below the drilling motor (via pipe sections, drill collars, or other structural members as known in the art) or may be directly connected to the downhole motor, if desired. Drilling fluid, which is commonly called drilling mud, is circulated through the pipe string and the motor to generate torque within the motor for causing the rotary drill bit to rotate. Then, the drilling fluid is returned to the surface through the annular space between the drilled borehole and the drill string and may carry the cuttings of the subterranean formation to the surface. Further, as known in the art, downhole drilling motors may include thrust bearings. More particularly, conventional downhole drilling motors include a stator that does not rotate and is connected to a housing of the motor and a rotor that rotates with the output shaft of the downhole fluid motor. In one embodiment, the stator and the rotor are each provided with a plurality of hard bearing surfaces such as diamond elements. The stator and rotor are positioned adjacent one another so that the diamond bearing surfaces of the rotor and stator contact one another.
Conventional bearing apparatuses typically include bearing surfaces that may interlock or damage one another in response to relative sliding movement between the bearing surfaces. Examples of conventional diamond thrust bearings are disclosed by U.S. Pat. Nos. 4,410,054, 4,468,138, and 5,092,687. More specifically, FIG. 1 shows a partial, enlarged, schematic view of one embodiment of conventional bearing surfaces 114 and 154 of tables 118 and 158, wherein bearing surfaces 114 and 154 are positioned adjacent (i.e., at least partially contacting) one another. As shown in FIG. 1, conventionally, tables 118 and 158 may comprise superhard grains 170 and catalyst 172 (e.g., a catalyst). Further, the average size of the superhard grains 170 of each of tables 118 and 158 may be substantially similar. Furthermore, contact between such conventional bearing surfaces may be detrimental. Explaining further, because superhard grains 170 are similarly sized, the superhard grains 170 of table 118 may at least partially interfere, interlock, or otherwise detrimentally interact with superhard grains 170 of table 158. For example, the exposed portions of superhard grains 170 of bearing surface 154 may fit at least partially in between the exposed portions of superhard grains 170 of bearing surface 114, or vice versa. Thus, such interlocking or interference between superhard grains 170 may cause damage to bearing surface 114, bearing surface 154, or both. In further detail, FIG. 2 shows three superhard grains 170, which are labeled G1, G2, and G3 and catalyst 172 of tables 118 and 158, respectively. As shown in FIG. 2, grains G1, G2, and G3 exhibit respective exposure distances E1, E2, and E3, respectively. As may be appreciated, superhard grain G1 may be positioned at least partially in between superhard grains G2 and G3 upon bearing surfaces 114 and 154 engaging one another. In addition, relative movement (e.g., along directions T1 and T2) may cause damage to at least one of diamond grains G1, G2, and G3. From the foregoing discussion, it may be appreciated that conventional bearing apparatuses (e.g., a rotor and a stator) including superhard materials comprising substantially similarly-sized (e.g., an average size) superhard grains may cause undesirable damage to the bearing surfaces of such apparatuses.
Thus, it would be advantageous to provide bearing apparatuses including bearing surfaces structured to inhibit interlocking or other detrimental interactions, systems including same, and related methods.